The patch titled
rcu: add a prefetch() in rcu_do_batch()
has been added to the -mm tree. Its filename is
rcu-add-a-prefetch-in-rcu_do_batch.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: rcu: add a prefetch() in rcu_do_batch()
From: Eric Dumazet <dada1@xxxxxxxxxxxxx>
On some workloads, (for example when lot of close() syscalls are done), RCU
qlen can be quite large, and RCU heads are no longer in cpu cache when
rcu_do_batch() is called.
This patch adds a prefetch() in rcu_do_batch() to give CPU a hint to bring
back cache lines containing 'struct rcu_head's.
Most list manipulations macros include prefetch(), but not open coded ones
(at least with current C compilers :) )
I got a nice speedup on a trivial benchmark (3.48 us per iteration instead
of 3.95 us on a 1.6 GHz Pentium-M)
while (1) { pipe(p); close(fd[0]); close(fd[1]);}
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
kernel/rcupdate.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletion(-)
diff -puN kernel/rcupdate.c~rcu-add-a-prefetch-in-rcu_do_batch kernel/rcupdate.c
--- a/kernel/rcupdate.c~rcu-add-a-prefetch-in-rcu_do_batch
+++ a/kernel/rcupdate.c
@@ -235,12 +235,14 @@ static void rcu_do_batch(struct rcu_data
list = rdp->donelist;
while (list) {
- next = rdp->donelist = list->next;
+ next = list->next;
+ prefetch(next);
list->func(list);
list = next;
if (++count >= rdp->blimit)
break;
}
+ rdp->donelist = list;
local_irq_disable();
rdp->qlen -= count;
_
Patches currently in -mm which might be from dada1@xxxxxxxxxxxxx are
git-net.patch
rcu-add-a-prefetch-in-rcu_do_batch.patch
-
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